We propose to evaluate the impact of representative components of dietary fiber, singly and in combination, on gastrointestinal function and microbiology and on bioavailability of micronutrients, especially vitamins, using the rat as an aminal model. The nature of the mechanism of fiber effects will be examined by comparisons of germ-free, conventional, and antibiotic-treated animals, by determining in vitro fiber-nutrient binding characteristics and by monitoring absorption and metabolism of micronutrients and other metabolites using radioactive tracer techniques. The role of the cecum of the rat in explaining fiber effects will be investigated by comparison with the cecectomized rat. Additional data will be collected regarding the role of fibers in the development and/or alteration of intestinal bacterial metabolism by monitoring enzyme activities and metabolites associated with microbial metabolism. Test fibers will include at least cellulose, pectin, lignin, guar gum, alginic acid, xylan and wheat bran. Nutrients under study will include at least zinc, iron, vitamin B-12, folacin and additional vitamins. It is expected that the data derived from these experiments will clarify principles which will be useful in evaluating the total impact of increasing the dietary fiber component of the human diet.